Enhanced Electrochemical Performance of Aprotic Li‐CO₂ Batteries with a Ruthenium‐Complex‐Based Mobile Catalyst

Abstract

Li-CO 2 batteries are regarded as next-generation high-energy-density electrochemical devices. However, the greatest challenge arises from the formation of the discharge product, Li 2 CO 3 , which would accumulate and deactivate heterogenous catalysts to cause huge polarization. Herein, Ru(bpy) 3 Cl 2 was employed as a solution-phase catalyst for Li-CO 2 batteries and proved to be the most effective one screened so far. Spectroscopy and electrochemical analyses elucidate that the Ru II center could interact with both CO 2 and amorphous Li 2 C 2 O 4 intermediate, thus promoting electroreduction process and delaying carbonate transformation. As a result, the charge potential is reduced to 3.86 V and over 60 discharge/charge cycles are achieved with a fixed capacity of 1000 mAh g À1 at a current density of 300 mA g À1 . Our work provides a new avenue to improve the electrochemical performance of Li-CO 2 batteries with efficient mobile catalysts.

Understanding the electrochemical reaction mechanisms of precious metals Au and Ru as cathode catalysts in Li–CO2 batteries

“…22 In addition, the intermediate product of Li 2 C 2 O 4 has been experimentally observed as the nal discharge products with both Mo 2 C/CNTs and Ru(bpy) 3 Cl 2 as cathode catalysts. 12,16,23 ) are reported to be experimentally detected by in situ Raman characterization at the beginning of the discharge processes, but the peaks of oxalate are quickly replaced by the growing signals of carbonate and carbon during the subsequent reductions. 15 Likewise, Ru as the cathode catalyst possesses a relatively low charging voltage (3.6 V) in Li-CO 2 batteries, and the discharge product of Li 2 CO 3 is possible to be reversibly reacted with carbons to form original reactants on Ru surfaces.…”

“…22 In addition, the intermediate product of Li 2 C 2 O 4 has been experimentally observed as the final discharge products with both Mo 2 C/CNTs and Ru(bpy) 3 Cl 2 as cathode catalysts. 12,16,23 First-principles density functional theory calculations have been used to study the possible reaction mechanisms of Mo 2 C as cathode catalysts, demonstrating that Li 2 C 2 O 4 can be thermodynamically stabilized as the final discharge products and prevent the further decomposition of Li 2 C 2 O 4 into Li 2 CO 3 . 24 However, when Au catalyst are previously used as the cathode for Li–CO 2 battery, oxalate species (C 2 O 4 2− ) are reported to be experimentally detected by in situ Raman characterization at the beginning of the discharge processes, but the peaks of oxalate are quickly replaced by the growing signals of carbonate and carbon during the subsequent reductions.…”

Challenges and prospects of lithium–CO2batteries

“…Amines are broadly recognized as another kind of good scrubbing agents in CO2 capturing facilities, which could be served as a potential candidate in Li-CO2 batteries [101]. In addition, new types of RMs that can convert the solid Li2CO3 to be a soluble state are also welcome [46]. It should be pointed out that, whatever new solvents or additives will be selected for the Li-CO2 batteries, their influence on the lithium metal anode should be firstly understood and characterized, in order to minimize the potential side reactions and achieve stable and reversible Li-CO2 batteries.…”

“…Batteries in ((e) and (f)) were discharged to 1,000 mAh•g −1 .Shallow or deep discharge herein denote that the batteries were discharged to 1,000 or 10,000 mAh•g −1 , respectively. Reproduced with permission from Ref [46],. © Wiley-VCH Verlag 2021.…”

Redox Mediator-Enhanced Performance and Generation of Singlet Oxygen in Li–CO2 Batteries

“…Among various catalysts that have been explored, redox mediators (RMs) as soluble catalysts are more effective by guaranteeing a better contact between the catalysts and insoluble product, therefore, promoting the reversibility of the battery compared with solid catalysts that involved solid–solid interactions during the electrochemical reaction. Relevant reports on the use of RMs as a catalyst in the construction of Li–CO 2 batteries, however, are limited so far. − …”